The present invention relates to an LSI package in which large scale integrated circuits (LSIs) for use in computers and other electronic apparatuses are installed in high density and a manufacturing method thereof, and more particularly to an LSI package having a built-in terminal resistor and a manufacturing method thereof.
In recent years, most of the main functional blocks of electronic apparatuses including computers above all, other data processing equipment and communication systems have come to be incorporated into LSIs to meet the need for ever faster processing. If LSIs become even larger in the scale of integration to enable a plurality of functional blocks to be incorporated into a single LSI chip, wiring between functional blocks will be shortened to further enhance the overall processing speed of the apparatus.
On the other hand, available industrial technology limits the extent of enhancing the scale of circuit integration and, from the viewpoint of economic optimization, the plurality of functional blocks constituting an electronic apparatus are divided into a plurality of LSI chips, which are arranged in high density to minimize the distances between them and thereby to increase the processing speed of the apparatus.
In particular, what consist of bare LSI chips, not encased, installed on a small wiring board at minimized spacing are known as an LSI package (typical of which is a multi-chip module, abbreviated to MCM). This configuration is being increasingly applied as a technique to reduce the wiring distances between LSI chips and thereby to effectively achieve faster processing by electronic apparatuses. One example is disclosed in Rao R. Tummala et al., Microelectronics Packaging Handbook, 1989, Van Nostrand Reinhold, pp. 786-790.
In such an LSI package, circuits linking LSI chips, which should ideally be accommodated within the LSI chips themselves, span the spaces between the LSI chips, and accordingly are required to permit significantly high speed. At present, square wave signals of tens to hundreds of MHz are used for transfers over these circuits.
To drive such LSI chip circuits in an LSI package, emitter coupled logic (ECL) output circuits of emitter follower type or gunning terminal logic (GTL) output circuits of source follower type, both capable of operating at high speed and having a large load driving capacity, are used.
In signal wiring connected to such output circuits (ECL circuits and GTL circuits), reflection occurs at ends, and transferred signals are distorted by multiple reflection. Therefore, in high speed signal transfers, signal wiring should be terminated with intrinsic impedances.
In an LSI package, generally, 10 to 100 LSI chips are mounted on a wiring board. As the wiring board is rectangular, having 6 to 15 cm long sides, the signal wiring length between LSI chips is 10 to 30 cm. Accordingly, when driving with LSI chips whose pulse rise characteristic is no more than 1 ns, terminal resistors are indispensable.
According to the prior art, such terminal resistors are either arranged on the wiring board surface as independent chips along with LSI chips or formed in advance on the wiring board as described in the Gazette of the Japanese Patent Laid-open No. 119047 of 1989 or that of the Japanese Patent Laid-open No. 227561 of 1991.
As stated above, terminal resistors provided on an LSI package, according to the prior art, are either arranged on the wiring board surface as independent chips along with LSI chips or formed in advance on the wiring board.
As the corresponding area of the wiring board surface is occupied by the terminal resistance elements in either of these manners, the distances either between adjoining LSI chips or between the terminal resistors and input/output circuits of the LSI chips are extended, resulting in cumbrance to high speed signal transfers. Therefore, the prior art involves the problem that the benefit of using an LSI package in an electronic apparatus (the benefit of increasing the processing speed of the electronic apparatus in which the LSI package is used) cannot be fully realized.
An object of the present invention is to provide, in view of the above-stated problem, an LSI package (LSI package with built-in terminal resistors), typically an MCM, which makes it possible to reduce the area of the wiring board surface occupied by terminal resistors, to position the terminal resistors close to input/output terminals of LSI chips and thereby to transfer signals at high speed. Another object of the invention is to provide a method to manufacture such LSI packages with built-in terminal resistors.